A&P2 Week 2: Heart

What is "normal" BP?

120/80

How does the heart keep its rhythm?

A coordinated heartbeat is a function of both the presence of gap junctions (allowing the passage of ions) and the conducting system, a network of non-contractile (autorhythmic) cells.

What is an electrocardiogram (ECG or EKG)

A device used to record and graph the electrical activity of the heart. The picture is drawn by a computer from information supplied by electrodes.

What is the vasomotor center?

A portion of the medulla oblongata (with cardiac and respiratory center) that regulates blood pressure and other homeostatic processes.

What is the cardiac center?

A portion of the medulla oblongata (with vasomotor and respiratory center) that receives impulses from baroreceptors and sends impulses to sympathetic and parasympathetic nervous systems.

Explain the role of capillary hydrostatic pressure and blood colloidal osmotic pressure on net filtration pressure in capillary filtration.

A small rise in capillary pressure causes an exponental increase in net filtration pressure which results an amount of fluid that is too much for the lymphatics to carry away. As a result, fluid begins to accumulate in the tissues, and edema occurs. If capillary pressure is very low, net reabsorption into the blood increases at the expense of the tissue fluid volume. Increasing or decreasing the protein concentration in the blood also affects the exchange.

How do ACE-inhibitors work to control blood pressure?

ACE inhibitors block production of angiotensin II, a vasoconstrictor. This lowers BP.

Name two acute conditions that significantly weaken the heart, and can result in death:

Angina pectoris: thoracic pain caused by fleeting deficiency in blood delivery to myocardium. Weakens heart cells. Myocardial infarction: Prolonged coronary blockage. Areas of cell death repaired with non-contractile scar tissue.

What is this picture? List: Superior vena cava Ascending aorta (cut open) Right ventricle anterior wall (retracted) Pulmonary trunk Pulmonary valve Aortic valve Trabeculae carneae Opening to right atrium Right ventricle Left ventricle Chordae tendinae Papillary muscles

Anterior view of a heart (pericardium intact) showing internal gross anatomical features.

What is this picture? List: Aortic arch (fat covered) Auricle of right atrium Auricle of left atrium Pulmonary trunk Anterior interventricular artery Apex of heart (left ventricle) Right ventricle

Anterior view of a heart (pericardium removed) showing external gross anatomical features.

Describe the three subtypes of arteries and veins, their structure and function.

Aorta, Arteries, arterioles Large vein, medium vein, venuole Both join into capillary beds.

What is the location and function of the cardiac arteries?

Arise from base of aorta (supply varies among individuals) and contain many anastomoses (junctions). Provide additional routes for blood delivery but cannot compensate for coronary artery occlusion

Where can the coronary sulcus be found?

At the root of the pulmonary trunk. It is a fat and vessel-filled groove supplying blood to the heart itself. On the posterior surface of the heart, the coronary sulcus contains the coronary sinus.Also called coronary groove, auriculoventricular groove, atrioventricular groove, AV groove.

What is the difference between atria and ventricles?

Atria are superior to ventricles, but ventricles are located at the apex of the heart (left one forms it).

What causes the P wave?

Atrial depolarization, initiated by the SA node.

Name the two types of valve found in the heart:

Atrioventricular (AV) valves and semilunar (SL) valves.

Explain the sources of intracellular calcium involved in cardiac muscle contraction, and review (just the basics of) actin/myosin/troponin/tropomyosin in contraction.

Cardiac cells utilize extracellular calcium for activation of cross bridge binding. Ca ions serve as "trigger" for muscle contraction by removing inhibition (troponin molecules). Ca ions travel through gap junctions / intercalated disks. Cardiac muscle fibers contract via excitation-contraction coupling (converting an electrical stimulus into a mechanical response), using a unique mechanism: calcium-induced calcium release. CICR involves the conduction of calcium ions into the cardiomyocyte, triggering more ions to the cytoplasm. Contraction in cardiac muscle follows the sliding filament model of contraction. Skeletal muscle: motor neuron action potential, neurotransmitter release, muscle cell action potential, release of calcium ions from SR, ATP-driven power stroke, sliding of myofilaments.

Compare and contrast the relative refractory period of skeletal muscle membranes and cardiac muscle membranes.

Cardiac muscle cells have a long absolute refractory period (200-250 ms); skeletal muscles have shorter absolute refractory period (1-2 msec) Skeletal: refractory periods are short enough to allow restimulation before the end of the muscle cell contraction as this allow for summation (increasing force production) and ultimately tetanus. Cardiac: refractory period doesn't end until almost the end of the relaxation period (all cardiomyocytes contract as unit), summation and tetanus is prevented from occurring.

Compare and contrast an action potential in a skeletal muscle and a cardiac muscle cell. Focus on the types of ion channels involved in the action potential, and the consequences these channel activities have on the AP.

Cardiac: action potentials spread from one muscle cell to the next, causing a series of synchronized contractions. (act as a syncytium).

What is the location and function of the cardiac veins?

Collect blood from capillary beds. Coronary sinus empties into right atrium. Several anterior cardiac veins empty directly into right atrium anteriorly.

What are arterial anastomoses? Describe their function.

Connection or loop between arteries, results in many blood vessels serving the same area of tissue. Almost all joints receive anastomotic blood supply, or blood supply from more than one source, serves as backup route in case of injury or blockage to vessel.

List the different types of capillaries. Where would you find each type of capillary? What types of materials will pass through each type of capillary?

Continuous, in skin and skeletal muscle - allow small molecules, water and ions, to pass. Fenestrated, in intestines and kidneys - allow small molecules and limited proteins. Sinusoidal, in liver, spleen, bone marrow - allows R & WBC and some protiens through.

Define systolic and diastolic blood pressures.

Diastolic pressure occurs near the beginning of the cardiac cycle and is the minimum pressure in the arteries as the ventricles fill with blood. Systolic pressure, or peak pressure, occurs when the ventricles contract near the end of the cardiac cycle and blood leaves the heart.

Why is this difference so important?

Different refractory periods we can either allow for tetanus to occur (in skeletal muscle) or prevent it from occurring (in cardiac muscle).

What are the structural and functional differences between arteries, veins, and capillaries?

Direction of blood flow, veins have valves (and pulmonary artery), thickness of wall, O2 content, colour, location. Capillaries don't function as individuals. Instead they form interweaving capillary beds. The micro-circulation — the arterioles, capillaries, and venules —constitutes most of the area of the vascular system and is the site of the transfer of O2, glucose, and enzyme substrates into the cells. Arteries and veins move products and wastes around the body.

How is mean arterial pressure (MAP) calculated from systolic and diastolic pressure?

Double the diastolic blood pressure and add the sum to the systolic blood pressure. Then divide by 3. For example, if a patient's blood pressure is 83/50, his MAP would be 61 mmHg

What is the function of the AV valves? What other structures assist (and how do they assist) the valves in their function?

Ensure unidirectional blood flow Open/close in response to pressure changes Chordae tendineae anchor cusps to papillary muscles

Which three layers of tissue make up the heart wall?

Epicardium, myocardium, and endocardium.

What are auricles?

Flaplike structures that increase the volume of atria.

Which part of an ECG indicated ventricular depolarization is complete?

Flat part between S and T

When does the heart receive oxygenated blood?

Functional blood supply to heart muscle is delivered when the heart is relaxed. Left ventricle receives most of the blood supply.

What is coronary circulation?

Functional blood supply to heart muscle itself Delivered when heart relaxed Left ventricle receives most blood supply Arterial supply varies among individuals Contains many anastomoses (junctions) Provide additional routes for blood delivery but cannot compensate for coronary artery occlusion

What is the common name for a myocardial infarction?

Heart attack.

If you were presented with a slide of muscle tissue, how would you determine it was cardiac muscle and not skeletal or smooth muscle?

Heart muscle is the only type with intercalcated discs; the cells almost always have only one nucleus; cells show some branching.

Where is the myocardium found? What does it consist of?

Heart muscle tissue / cardiac muscle and connective tissue that forms concentric layers around atria or spirals within ventricle walls.

What are myogenic controls?

How arteries and arterioles react to an increase or decrease of BP to keep a constant blood flow within the vessel.

What is hypotension? Hypertension? What are the factors that contribute to hypertension?

Hypotension is low blood pressure; Hypertension is high blood pressure.

Name two valve conditions that significantly weaken the heart:

Incompetent valve: blood backflows, so heart re-pumps same blood over and over. Valvular stenosis: "stiff flaps" constrict opening so heart must exert more force to pump same amount of blood.

What is unique about the pulmonary artery?

It carries deoxygenated blood.

What is coronary circulation?

It describes the flow of blood to the heart itself.

How does the amount of blood differ between the pulmonary and systemic circuits?

It doesn't. The heart pumps equal volumes of blood to the pulmonary and systemic circuits; difference is in the distance.

Describe blood's pathway through the AV valves ONLY from when it returns to the heart.

It fills the atria, pressing against the AV valves. Increased pressure forces AV valves open as atrial pressure is greater than ventricular pressure. As ventricles fill, AV valve flaps hang limply into ventricles. Atria contract, forcing additional blood into ventricles. Ventricles contract, forcing blood against AV valve cusps. Atrial pressure less than ventricular pressure. AV valves close. Papillary muscles contract and chordae tendineae tighten, preventing valve flaps from everting into atria.

Where is the endocardium found? What does it consist of?

It is the innermost layer of the heart. The endothelium is in contact with the chambers of the ventricles, then a layer of areolar tissue.

Where is the pericardium found? What does it consist of?

It lines the cavity of the heart. Superficial fibrous pericardium Deep two-layered serous pericardium It encloses a fluid-filled pericardial cavity.

What connects the aortic arch and the left pulmonary artery?

Ligamentum arteriosum

What is MAP?

Mean Arterial Pressure.

Where and how is arterial blood pressure taken?

Measured using an instrument called a sphygmomanometer, or BP cuff. Wrapped at brachial artery on arm, inflated until artery squeezed closed, and its blood flow stopped. Deflation occurs. When the cuff pressure equals the systolic blood pressure of the brachial artery, it opens enough for a small amount of blood to spurt through. This produces a sharp sound (Korotkoff's sound) that can be heard through the stethoscope. The height of the mercury column when this first tapping sound is heard represents the arterial systolic pressure (SP).

How is the heartbeat adjusted by the body?

Modified by ANS (autonomic nervous system) via cardiac centers in medulla oblongata.

Describe neural regulation of the CV system.

Neurological regulation of blood pressure and flow depends on the cardiac and vasomotor centers in the medulla oblongata. These neurons respond to changes in BP as well as blood concentrations of gases and certain ions.

List some of the molecules/chemicals that induce localized vasodilation or vasoconstriction. Which mechanism controls this?

Nitric oxide (NO) - has brief but potent vasodilator effects Atrial natriuretic peptide (ANP) - vasodilation Antidiuretic hormone (ADH) - vasoconstriction Angiotensin II - causes vasoconstriction Norepinephrine acting on alpha receptors causes vasoconstriction. Epinephrine - can cause vasodilation in skeletal muscle during exercise Erythropoietin (EPO) - vasoconstriction The autoregulatory mechanism / SNS and PNS.

What is the foramen ovale?

Normal cardiac structure of fetus and neonate; best described as a "door" between the right and left atria. Essential for fetal circulation (fetuses can't breathe); directs oxygenated, nutrient-rich blood from placenta to the developing brain.

Explain what phases of the cardiac cycle are represented by systole/diastole.

One cycle of cardiac activity is divided into two phases - diastole and systole. Diastole represents the period of time when the ventricles are relaxed (not contracting). At the end of diastole, both atria contract, which propels an additional amount of blood into the ventricles. Systole represents the time during which the left and right ventricles contract and eject blood into the aorta and pulmonary artery, respectively - AV valves are closed but SL valves are open. Close at end of systole.

Where is the epicardium found? What does it consist of?

Otherwise known as visceral pericardium; outermost layer (mesothelium) in contact with the fluid of the pericardial cavity, then a layer of areolar tissue.

Where can the coronary sinus be found? What is it?

Posterior surface of the heart. Inside coronary sinus.

List the four ways angiotensin II affects blood pressure.

Potent vasoconstrictor, increasing peripheral resistance. Stimulates release of aldosterone, a hormone causing renal sodium absorption and subsequent sodium flow into blood, followed by water to maintain volume. Stimulates release of ADH which promotes water absorption by kidneys Increases thirst sensation via hypothalamus thirst center.

What are the two circuits along which blood flows?

Pulmonary and systemic circuit.

What are the differences in pressure and friction between the pulmonary and systemic circuits? What is the physiological result?

Pulmonary circuit: short, low-pressure circulation Systemic circuit: long, high-friction circulation Left ventricle walls of heart are 3x thicker than right and take up more space; also form entire apex of heart.

What is pulse pressure?

Pulse pressure is the difference between the systolic (higher) and diastolic (lower) pressure readings.

What are the factors that contribute to resistance in a blood vessel?

Resistance is due to the width of the vessels, it's hard to push a lot of blood through a narrow tube. Turbulent blood flow (as opposed to laminar). Laminar blood flow is direct, turbulent blood flow has eddy currents which add friction. Causes of turbulence include arterial plaque deposits and

Describe conduction through the heart (5 steps).

SA node activates and atrial activity begins. Stimulus traverses atrial surface to AV node. 100msec delay at AV node; atrial contraction begins. Impulse travels along interventricular septum to AV bundle, bundle branches, Purkinje fibers, and, via moderator band, to papillary muscles of r. ventricle. Impulse delivered by Purkinje fibers and relayed to the ventricular myocardium. Atrial contraction completes, ventricular contraction begins.

Which direction does fluid move on each end of the capillary bed and why?

Since water exiting capillaries carries molecules of dissolved substances, capillary blood first unloads materials for the tissues at the arterial end and then picks up materials for transport at the venous end. The direction of fluid movement depends on opposing forces of blood pressure and osmotic pressure. Hydrostatic blood pressure, exerted by the heart, tends to force water out of the capillaries and osmotic pressure, reflecting a difference in protein concentrations, tends to draw water into the capillaries. As arterioles become capillaries, frictional resistance and increased cross-sectional area lower blood pressure, forcing fluids out of capillaries and into tissue fluid. This concentration of proteins means the blood is hypertonic to the tissue fluid, resulting in water moving into the capillaries from the tissue fluid by osmosis, so there's not a steady loss of fluid from the bloodstream.

Describe the function of venous valves.

Stop backflow of blood in low pressure venous system, especially when working against gravity.

Which nerves increase heart rate?

Sympathetic cardiac nerves.

How does systemic BP differ from capillary and venous BP?

Systemic blood pressure is pressure exerted on blood vessels in systemic circulation. Measured using the arterial pressure, or pressure exerted upon arteries during heart contractions. Much stronger.

What can abnormal SA node activity cause?

Tachycardia; bradycardia

Understand the effects of hormones on BP. Which mechanism controls this?

The adrenal medulla hormones, norepinephrine and epinephrine, increase blood pressure. Antidiuretic hormone (ADH) - causes intense vasoconstriction in cases of extremely low BP. ANP - protien hormone secreted by heart muscle cells Hormonal Regulation.

What are the three different mechanisms for controlling blood pressure?

The autoregulatory, neural and hormonal regulation systems , Epo, and

If you were looking at an adult heart, what would you see instead of a foramen ovale?

The fossa ovalis. Foramen ovale closes at birth when the lungs become functional. Pulmonary pressure decreases; the left atrial pressure exceeds that of the right. This forces the septum primum against the septum secundum, functionally closing the foramen ovale. In time the septa eventually fuse, leaving a remnant called the fossa ovalis.

Describe the structure of the heart.

The heart is a single organ, comprised of two side-by-side pumps.

How does blood flow relate to pressure and resistance?

The higher the pressure exerted by the heart, the faster blood will flow. This is a direct relationship. The more resistance exerted by the vessels, the slower blood will flow. This is an inverse relationship.

Why does the left ventricle have such a thick muscular wall while the right ventricle does not?

The left ventricle pumps blood to the entire body; the right pumps blood only to the lungs.

What other system is involved in recapturing fluid lost from the circulatory system?

The lymphatic system.

What is hydrostatic pressure?

The pressure exerted by fluids, such as blood and tissue fluid, against the walls of the capillaries.

Which side of the heart receives low-oxygen blood, and which receives high-oxygen blood? From where?

The right side receives low-oxygen blood from tissues and the left side receives high-oxygen blood from the lungs.

What are the three layers of blood vessels?

The tunica intima on the inside, the tunica externa on the outside, and the tunica media between the two.

What are the mechanisms by which blood returns to the heart via the venous system?

The venous system (which is very low pressure) is part of a closed circuit - venous return equals cardiac output. Muscle contraction (of veins near skeletal muscle), respiratory activity (inspiration), and valves preventing backflow assist return.

Where are AV valves found?

There are two. Mitral (bicuspid, left AV valve) and tricuspid (right AV valve) valves, located between upper atria and lower ventricles.

What is the function of the semilunar valves?

There are two: aortic semilunar valve and pulmonary semilunar valve. They act to prevent backflow of blood from the arteries to the ventricles (into the heart), also help maintain pressure of major arteries. The aortic semilunar valve separates the left ventricle from the opening of the aorta.

What are the intereventricular sulci? Where are they?

There is a posterior and an anterior interventricular sulcus.

What are autorhythmic cells?

They have unstable resting membrane potentials (pacemaker potentials or prepotentials)

What is a baroreceptor for?

They sense the blood pressure and relay the information to the medulla, so correct blood pressure is maintained. These stretch receptors are located in the blood vessels of all vertebrate animals. If BP falls, baroreceptor firing rate decreases and SNS reflexes act to help restore blood pressure by increasing heart rate.

What is the role of chemoreceptors in the medulla oblongata?

To detect changes in blood acidity. If the blood is too acidic, medulla oblongata sends electrical signals to intercostal and phrenical muscle tissue increasing their contraction rate in order to reoxygenate the blood.

What can defects in the intrinsic conduction system cause?

Uncoordinated atrial and ventricular contractions Arrhythmias - irregular heart rhythms Fibrillation - rapid, irregular contractions

Which nerve decreases heart rate?

Vagus nerve (parasympathetic system).

What does the QRS complex represent?

Ventricular depolarization begins at the heart's apex, causing the QRS complex. Atrial repolarization occurs.

What causes the T wave?

Ventricular repolarization beginning at apex of heart.

Explain the Renin-Angiotensin pathway.

When systolic blood pressure falls to 100 mm Hg or lower, kidneys release enzyme renin into bloodstream. Renin splits angiotensinogen, a large protein present in the bloodstream, into pieces. One piece is angiotensin I. Relatively inactive angiotensin I is split by angiotensin-converting enzyme (ACE). One piece is angiotensin II, a very active hormone, which causes smooth muscle of arterioles to constrict, increasing blood pressure. It also triggers aldosterone release from adrenal glands and antidiuretic hormone (ADH) from pituitary gland. Aldosterone and ADH cause the kidneys to retain sodium. Aldosterone also causes kidneys to excrete potassium. The increased sodium causes water to be retained, increasing blood volume and BP.

What is an electrical event, in the context of the cardiovascular system?

When the heart depolarizes and contracts without nervous or hormonal stimulation. Rhythm can be altered by autonomic nervous system.

What are precapillary sphincters? Describe their function.

Where a capillary originates from an arteriole, a smooth muscle fiber encircles it, forming a ring of muscle that opens and closes the entrance to the capillary, adjusting blood flow. If the sphincter is damaged or cannot contract, blood can flow into the capillary bed at high pressures, causing damage.

How does the graph show the impulse is delayed at the AV node?

With atrial depolarization complete, the graph is baseline flat.

Can human heart valves be replaced?

Yes. With a mechanical, animal, or cadaver valve.

Define automaticity. What % of heart cells have it?

~1% of cardiac cells have automaticity (autorhythmicity), meaning they do not need nervous system stimulation. Can depolarize entire heart